This research proposal is a supplement to our existing lymphocyte biology grant NIH PO1 AI 11851. It is essential for us to maintain this colony to continue a number of ongoing projects including Virus Infection and Altered MHC Products, Structural Studies of Products of the l7th Chromosome in the Mouse, Differentiation of Cytotoxic T Cells, and Role of Qa-2 as a Target Antigen in CML.